This invention relates to a device for converting an electric signal into an acoustic signal comprising an input terminal for receiving an electric input signal, an electro-acoustic transducer unit, and an amplifier circuit for driving the electro-acoustic transducer unit, which amplifier circuit comprises an input coupled to the input terminal and an output coupled to the electro-acoustic transducer unit. The invention also relates to an amplifier circuit for driving an electro-acoustic transducer unit. Known devices of this type generally comprise a transducer unit whose quality factor is at least substantially equal to 1. The known transducer unit has a frequency-response characteristic which is comparatively flat in a frequency range between the resonant frequency of the transducer unit and the break-up frequency of the transducer unit, for which reference is made to "Theory and numerical calculation of the vibration and sound radiation of cone and dome loudspeakers with non-rigid diaphragms", preprint No. 1437 (D-1) of the 62.sup.th Convention of the Audio Engineering Society, held from 13 to 16.sup.th of March 1977 in Brussels, in particular FIGS. 5a and 6.
Such transducer units are driven by amplifier circuits (amplifiers) which have a flat frequency-response characteristic. However a drawback of, the known device is its relatively low efficiency, which is defined as the ratio of the acoustic output power of the transducer unit to the electric input power applied to the input terminal.